Organic light emitting diode and method of manufacturing

ABSTRACT

Aspects of the present disclosure provide for manufacturing an organic light emitting diode (OLED) by forming two terminals of the OLED on two substrates of the display, and then depositing a plurality of layers of the OLED on one or both of the two terminals to form a first portion and a second portion of the OLED on each substrate. The two portions are joined together to form an assembled OLED. The deposition of the two portions can be stopped with each portion having approximately half of a common layer exposed. The two portions can then be aligned to be joined together and an annealing process can be employed to join together the two parts of the common layer and thereby form the OLED.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of and claims priority to U.S. patent application Ser. No. 13/561,411, filed Jul. 30, 2012, now allowed as U.S. Pat. No. 8,901,579, which claims the benefit of U.S. Provisional Application No. 61/514,886, filed Aug. 3, 2011, each of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present disclosure generally relates to organic light emitting diodes, particular to methods of manufacturing organic light emitting diodes for use in displays such as active matrix organic light emitting diode displays.

BACKGROUND

Displays can be created from an array of organic light emitting diodes (“OLEDs”) each controlled by individual circuits (i.e., pixel circuits). The individual circuits have transistors for selectively controlling the circuits to be programmed with display information and to emit light according to the display information. OLEDs are emissive display devices which generally emit light according to the amount of current driven through the OLED. OLEDs generally include a light emitting region where positively charged holes meet with electrons. Light is emitted as the electrons are captured by the holes and settle at a lower energy state. The amount of current driven through the OLED is thus proportionate to the number of emission events, and the light emitted from an OLED is accordingly related to the current driven through the OLED. Thin film transistors (“TFTs”) fabricated on a substrate can be incorporated into such displays to control the amount of current driven through the OLEDs according to the display information programmed into the individual circuits.

OLEDs can be developed by sequentially depositing layers of material onto a substrate. Such a layering process generally commences and terminates with depositing conductive electrodes (i.e., terminals) such that a completed OLED includes a plurality of layers disposed between two electrodes. To connect the OLED to a TFT of a pixel circuit, an electrical connection is generally made between a terminal of the TFT and one of the electrodes of the OLED through a contact, which process leads to problems due to the precision of the required alignment between the contacts and the OLED terminal and the relative unreliability and inefficiency of the contacts formed.

Applying a voltage across the two electrodes in excess of an operating voltage associated with the OLED generally allows a current to flow through the device and for light to be emitted from an emission region of the OLED. As the OLED ages, the operating voltage of the OLED can shift (e.g., increase). The shift in the OLED operating voltage influences the voltage applied across the TFT, and thereby modifies the current flowing through the OLED, and thus influences the light output of the OLED.

It is desirable, therefore, to configure the pixel circuit such that the terminal of the TFT coupled to the OLED does not influence the voltage applied across the TFT. Such a structure is commonly referred to as a reverse OLED, because one way to develop the structure is to sequentially develop the layers of the OLED in the reverse order. One way to develop a reverse OLED is to start the deposition on the display substrate with the cathode terminal (“layer”) instead of the anode terminal (“layer”). However, suitable transparent materials for use as a cathode terminal with a suitably high work function are rare, unavailable and/or expensive. Furthermore, the performance of such devices as have been created is inferior to conventional OLED devices.

Another method for achieving the desired structure is to develop the normal OLED on encapsulation glass and develop a matching contact on the TFT substrate. The two substrates can then be put together. However, the contact quality between the OLED and the matching contact requires careful alignment and consistent pressure. The results across an entire display are not good and displays created with such techniques frequently contain many dead pixels and high voltage OLEDs due to the poor quality of the electrical path between the contact and the OLED.

SUMMARY

Aspects of the present disclosure provide an organic light emitting diode (“OLED”) which is prepared by depositing a first terminal on a first substrate, and a second terminal on a second substrate. A plurality of layers forming the inner region of the OLED between the first terminal and the second terminal is divided into a first portion and a second terminal. The first portion of the plurality of layers is then deposited on the first terminal and the second portion of the plurality of layers is deposited on the second terminal. The first substrate and the second substrate are then aligned and the first portion and the second portion are joined together.

The first portion of the plurality of layers can include a first part of a common layer, and the second portion of the plurality of layers can include a second part of the common layer. The first and second parts of the common layer can each be the last deposited of the first and second portions of the plurality of layers, respectively. The first portion and the second portion can be aligned such that the exposed surfaces of the two parts of the common layer meet at an intralayer interface. The two parts of the common layer are annealed together to form a unified common layer, and thereby join together the first and second portions of the OLED.

The foregoing and additional aspects and embodiments of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments and/or aspects, which is made with reference to the drawings, a brief description of which is provided next.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.

FIG. 1A illustrates a symbolic plan of a first portion of an organic light emitting diode.

FIG. 1B illustrates a symbolic plan of a second portion of an organic light emitting diode.

FIG. 2 is a flowchart of a process for forming an organic light emitting diode from two portions.

FIG. 3A illustrates a symbolic plan of a first and second portion of the organic light emitting diode while the two portions are aligned to be joined together.

FIG. 3B illustrates a symbolic plan of the organic light emitting diode shown in FIG. 3A following an annealing process to infuse the common layer together.

FIG. 4A is a flowchart of a process for forming an organic light emitting diode by annealing two parts of a common layer.

FIG. 4B illustrates a flowchart of a process similar to that shown in the flowchart in FIG. 4A, but further illustrating several aspects of the process performed in parallel.

FIG. 5A is a vertical section of an assembled first portion of an organic light emitting diode formed on an encapsulation substrate.

FIG. 5B is a vertical section of an assembled second portion of an organic light emitting diode formed on a TFT substrate and configured to join the first portion illustrated in FIG. 5A.

FIG. 5C is a vertical section of an organic light emitting diode formed by annealing a first part and a second part of a common layer of the first and second portions shown in FIGS. 5A and 5B.

FIG. 6A is a vertical section of a first portion of an organic light emitting diode similar to that shown in FIG. 5A and incorporating spacers.

FIG. 6B is a vertical section of a second portion of an organic light emitting diode similar to that shown in FIG. 5B and incorporating spacers.

FIG. 6C is a vertical section of an organic light emitting diode formed by annealing a first part and a second part of a common layer of the first and second portions shown in FIGS. 6A and 6B.

FIG. 7A is a vertical section of a first portion of an organic light emitting diode similar to that shown in FIG. 6A and incorporating banks.

FIG. 7B is a vertical section of a second portion of an organic light emitting diode similar to that shown in FIG. 6B and configured to be joined to the first portion illustrated in FIG. 7A.

FIG. 7C is a vertical section of an organic light emitting diode formed by annealing a first part and a second part of a common layer of the first and second portions shown in FIGS. 7A and 7B.

While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1A illustrates a symbolic plan of a first portion 2 of an organic light emitting diode. The first portion 2 is deposited on a first substrate 10 in sequentially developed layers. The first OLED terminal 12 is formed on the first substrate 10. For example, in an implementation where the first substrate 10 is a transparent substrate such as an encapsulation glass, the first OLED terminal can be an anode terminal formed of a transparent conductive material such as indium tin oxide (“ITO”). On the first OLED terminal 12, 0 to N layers 14 of the OLED are deposited. The 0 to N layers 14 can include, for example, a hole injection layer, a hole transfer layer, an emission layer, an electron transfer layer, an electron injection layer, and/or a planarization layer. The 0 to N layers 14 can also include no layers. Appropriately doped semiconductive, organic, and/or inorganic materials can be selected as appropriate for particular implementations of the OLED based on desired emission performance characteristics. Furthermore, one or more of the plurality of layers can be omitted and/or combined with other layers. The first portion 2 can optionally terminate with a first part 16 a of a common layer.

FIG. 1B illustrates a symbolic plan of a second portion 4 of an organic light emitting diode. The second portion 4 is formed similarly to the first portion 2. The first portion 4 is deposited on a second substrate 22. For example, the second substrate 22 can be a glass planarization substrate over a terminal of a TFT. The second portion 4 includes a second OLED terminal 20. The second OLED terminal 20 can be a cathode terminal formed of a reflective metallic material having a high work function. On the second OLED terminal 20, 0 to M layers 18 of the OLED are deposited. The 0 to M layers 18 can include, for example, any of the plurality of layers recited for the 0 to N layers 14 in connection with FIG. 1A. The 0 to M layers 18 can also include no layers, in which case all of the plurality of layers of the OLED, other than the second OLED terminal 20, are developed on the first substrate 10. The second portion 4 can optionally terminate with a second part 16 b of the common layer. In implementations including the first part 16 a and the second part 16 b, the parts 16 a, 16 b jointly comprise the common layer of the OLED. The common layer can be any of the plurality of layers recited in connection with the 0 to N layer 14 or the 0 to M layer 18. For example, the common layer can be the electron transfer layer. In implementations incorporating the first part 16 a and the second part 16 b, the two parts can each be substantially equal to half of the common layer, or can be another complementary matched set of portions of the common layer such that the two parts 16 a, 16 b jointly form the common layer when the two parts 16 a, 16 b are joined together.

FIG. 2 illustrates a flowchart 30 of a process for forming an organic light emitting diode from two portions for use in a display. FIG. 2 will be described in connection with the first portion 2 and the second portion 4 illustrated in FIGS. 1A and 1B. The first portion 2 of the OLED is formed on a first substrate 10 of the display (32). The second portion 4 of the OLED is formed on a second substrate 22 of the display (34). To complete the preparation of the OLED, the first portion 2 and the second portion 4 are joined together (36).

FIG. 3A illustrates a symbolic plan of the first portion 2 and the second portion 4 of the organic light emitting diode while the two portions are aligned to be joined together. In the implementation shown in FIGS. 3A and 3B, the first portion 2 and the second portion 4 each include a respective first part 16 a and second part 16 b of the common layer, which is joined together by an annealing process (FIG. 3B) to infuse (“join”) the first portion 2 to the second portion 4. As shown in FIG. 3A, the first portion 2 is positioned such that the first part 16 a abuts the second part 16 b at an interface.

FIG. 3B illustrates a symbolic plan of the organic light emitting diode 6 shown in FIG. 3A following an annealing process to infuse the common layer 16 together. The first part 16 a and the second part 16 b are subjected to annealing, which can include thermal, pressure, or optical (e.g., laser) annealing. The resulting common layer 16 is a unitary layer. By terminating the first portion 2 and the second portion 4 near a mid-point of the common layer 16, such that the annealing process infuses an intralayer interface of the common layer, the annealing process avoids any interlayer interfaces. Interlayer interfaces can be more critical to the performance of the OLED than annealed intralayer interfaces, and therefore interlayer interfaces (e.g., the interfaces between the plurality of layers in the 0 to N layers 14 and/or the 0 to M layers 18) are advantageously formed by the layered deposition process rather than by an annealing process.

FIG. 4A is a flowchart 40 of a process for forming an organic light emitting diode for use in a display by annealing two parts of a common layer. A first terminal (e.g., the first terminal 12) is formed on a transparent substrate (e.g., a transparent encapsulation glass) of a display (42). 0 to N layers (e.g., the 0 to N layers 14) of the OLED are developed on the first terminal (44). The 0 to N layers are sequentially deposited on the first terminal. The 0 to N layers can include, for example, a hole injection layer, a hole transfer layer, an emission layer, an electron transfer layer, an electron injection layer, and/or a planarization layer. In addition, one or more of the layers can be omitted and/or combined with other layers. In an example, the 0 to N layers can include a hole injection and transfer layer, formed on the first terminal, and an emission layer, formed on the hole injection and transfer layer. A first part of a common layer (e.g., the electron transfer layer) is then developed on the 0 to N layers (46).

FIG. 4B is a flowchart 40′ of a process similar to that shown in the flowchart in FIG. 4A, but further illustrating several aspects of the process performed in parallel. In particular, FIG. 4B illustrates that forming the first portion (e.g., the first portion 2) of the OLED on the transparent substrate (42, 44, 46) can be carried out in parallel with forming the second portion (e.g., the second portion 4) on the substrate of a drive TFT (48, 50, 52). Parallel operations can advantageously allow for faster production times. Following the parallel operations, the two portions are joined together by annealing the two parts of the common layer together (54). While the flowcharts 40 and 40′ are provided to illustrate two exemplary implementations of the present disclosure, the present disclosure is not limited to implementations where the various stages to develop the OLED are performed strictly serially or in parallel. Implementations of the present disclosure can be realized incorporating a combination of serial ordering and parallel ordering.

Next a schematic of a particular example of an OLED developed according to an example implementation of the present disclosure is described. The views shown in FIGS. 5A through 7C are generally cross sectional views of the first and second portions of the OLED, and the OLED after it has been infused (“joined”). The views schematically illustrate an example of the plurality of layers of the OLED, but the schematic views are for illustrative purposes and are not drawn to scale (e.g., the schematic illustrations are not intended to convey the relative thicknesses of the plurality of layers of the OLED).

FIG. 5A is a vertical section of a first portion 102 of an organic light emitting diode formed on an encapsulation substrate 60. The encapsulation substrate 60 has an enclosed side 62 and an exposed side 64. An anode terminal 66 is formed on the enclosed side 62 of the encapsulation substrate 60. The encapsulation substrate 60 and the anode terminal are each desirably substantially visually transparent to allow light from the OLED to be emitted through the exposed side 64. The anode terminal 66 can be formed from indium tin oxide (“ITO”) or a comparable conductive visually transparent material. The anode terminal 66 can be formed on the encapsulation substrate 60 by a deposition process to develop a layer of ITO (or comparable material) on the encapsulation substrate 60. A hole transfer and injection layer 68 is then developed (e.g., “deposited”) on the anode terminal 66. The hole transfer and injection layer 68 can be developed on the anode terminal 66 by a deposition process or a similar technique. An emission layer 70 is then developed on the hole transfer and injection layer 68. A first part 72 a of an electron transfer layer is developed on the emission layer 70. The first part 72 a of the electron transfer layer has an exposed first surface 74. The first part 72 a of the electron transfer layer is approximately half of the thickness of the full electron transfer layer (72 in FIG. 5C). The development of the first portion 102 is halted with the exposed first surface 74.

FIG. 5B is a vertical section of a second portion 104 of the organic light emitting diode formed on a TFT substrate and configured to join the first portion 102 illustrated in FIG. 5A. A planarization substrate 82 is developed on a drain terminal 84 of the TFT. The planarization substrate 82 is formed with an aperture 85 such that at least a portion of the drain terminal 84 remains exposed through the planarization substrate 82. A cathode terminal 80 is then developed (e.g., “deposited”) on the aperture 85 such that the cathode terminal 80 is securely electrically coupled to the drain terminal 84 of the TFT. An electron injection layer 78 is then developed on the cathode terminal 80. The second part 72 b of the electron transfer layer is then developed on the electron injection layer 78. The second part 72 b of the electron transfer layer can be approximately half of the electron transfer layer such that the first part 72 a and the second part 72 b together form the full electron transfer layer. The second part 72 b includes an exposed second surface 76. The development of the second portion 104 is halted with the exposed second surface 76 of the second part 72 b.

The development of the plurality of layers 66, 68, 70, 72 a, 72 b, 78, 80, 82 of the first portion 102 and the second portion 104 can each be formed by a deposition process or similar technique for forming thin films of material.

FIG. 5C is a vertical section of an organic light emitting diode 106 formed by annealing the first part 72 a and the second part 72 b of the electron transfer layer shown in FIGS. 5A and 5B. The first portion 102 is positioned such that the exposed first surface 74 of the first part 72 a of the electron transfer layer abuts the exposed second surface 76 of the second part 72 b of the electron transfer layer. The interface between the exposed surfaces 74, 76 is thus an intralayer interface, and the two parts 72 a, 72 b can be infused (“joined”) by annealing the two parts 72 a, 72 b together to form the unitary electron transfer layer 72. The annealing can be accomplished by a thermal annealing process at, for example, 200 to 300 degrees Celsius.

An exemplary operation of the OLED 106 illustrated schematically in FIG. 5C is described next. In operation, the TFT begins to drive a current to flow generally toward the drain terminal 84, such that the cathode terminal 80 acquires a negative voltage with respect to the anode terminal 66. Once the voltage difference between the cathode terminal 80 and the anode terminal 66 is sufficient to exceed an operating voltage (i.e., “on voltage”) of the OLED, electrons injected in the electron injection layer 78 from the cathode terminal 80. The injected electrons are urged generally away from the cathode terminal 80 toward the emission layer 70, which can be considered a recombination layer. At the same time, positively charged holes are injected from the anode terminal 66 and transferred through the hole injection and transfer layer 68. The holes are urged generally away from the anode terminal 66 toward the emission layer 70.

In the emission layer, the electrons generally occupy the lowest unoccupied molecular orbital level (LUMO) in the emission layer 70 until recombining with a hole. The recombined electrons radiatively decay to the highest occupied molecular orbital level (HOMO) in the emission layer 70, and light is emitted according to the accompanying change in energy. The light emitted from the emission layer 70 passes through the encapsulation substrate 60 to emerge from the exposed side 64 of the encapsulation surface. Light that is initially directed away from the encapsulation surface 60 (e.g., toward the cathode terminal 80) is desirably reflected by the cathode terminal 80 to be emitted through the encapsulation surface 60. The cathode terminal 60 is advantageously formed from a reflective substance, such as a metallic material. The cathode terminal 80 is also advantageously selected to have a work function suitable to injection electrons having an energy sufficient to occupy the LUMO in the emission layer 70. Thus, the material characteristics of the emission layer 70 (e.g., HOMO and LUMO) can influence the selection of the cathode terminal 80, and also the anode terminal 66.

FIG. 6A illustrates a first portion 102′ of an organic light emitting diode similar to that shown in FIG. 5A, but incorporating spacers 112, 114. In the cross-sectional view of FIG. 6A, the spacers 112, 114 are placed on the opposing sides of the first portion 102′. The spacers 112, 114 are placed on the anode terminal 66 to avoid interrupting signals carried on the anode terminal 66, however, the spacers 112, 114 can be placed on other layers such as, for example, the hole injection and transfer layer 68. The spacers 112, 114 can completely surround the pixel area of the OLED and can include a plurality of columns and/or cylinders arranged horizontally and/or vertically with respect to the plane of the display. The spacers 112, 114 can be composed of materials including, for example, a nitrides and/or oxides. The spacers 112, 114 can advantageously provide a physical separation between layers of adjacent OLEDs developed on the encapsulation substrate 60. As described in connection with FIG. 6C, the spacers 112, 114 can also regulate the pressure applied to the OLED 106′ to prevent the OLED 106′ from being compacted (“crushed”) when the first portion 102′ and the second portion 104′ are joined together.

During manufacturing, the spacers 112, 114 can also assist in the alignment of a shadow mask which covers pixels not receiving deposited semiconductor layers. For example, when a patterned red, green, and blue configuration of pixels is being developed on the encapsulation substrate, the shadow mask can be placed over the display panel to provide small holes through which layers for particular colors can be deposited on the corresponding the pixel areas. By providing the spacers 112, 114, the shadow mask can rest on the spacers and avoid warping or stretching of the shadow mask when positioning it over the display panel.

FIG. 6B illustrates a second portion 104′ of an organic light emitting diode similar to that shown in FIG. 5B, but incorporating spacers 114, 116. Similar to the description of the spacers 112, 114 provided in connection with FIG. 6A, the spacers 114, 116 are placed (“positioned”) on the planarization substrate 82. The spacers 114, 116 are advantageously positioned to be aligned with the spacers 112, 114 of the first portion 102′ such that the spacers 114, 116 abut corresponding ones of the spacers 112, 114 when the first portion 102′ is joined to the second portion 104′.

FIG. 6C illustrates an organic light emitting diode formed by annealing a first part and a second part of a common layer of the first and second portions shown in FIGS. 6A and 6B. The OLED 106′ is similar to the OLED 106 shown in FIG. 5C, except that the OLED 106′ includes the spacers. As shown in FIG. 6C the respective spacers of the first portion 102′ and the second portion 104′ abut one another in the assembled OLED 106′ to protect the deposited layers of the OLED 106′ (e.g., the layers 70, 72, 78, 80) from being damaged due to compression during the joining of the two portions. Properly aligned at assembly, the spacer 114 of the first portion 102′ abuts the spacer 116 of the second portion 104′ and the spacer 112 of the first portion 102′ abuts the spacer 118 of the second portion 104′.

FIG. 7A illustrates a first portion 102″ of an organic light emitting diode similar to that shown in FIG. 6A and incorporating banks 122, 124. The banks 122, 124 are placed (“positioned”) on the anode terminal 66 to surround the hole injection and transfer layer 68. As shown in FIG. 7A, the bank structure provided by the banks 122, 124 prevent the first part 72 a of the electron transfer layer from abutting the hole injection and transfer layer 68. The bank structure thus contributes to the performance of the OLED 106″ by ensuring that the recombination events occur substantially within the emission layer 70 rather than in the regions where the electron transfer layer 72 directly abuts the hole injection and transfer layer 68. For example, FIGS. 5A and 6A provide examples where a sub-region of the electron transfer layer 72 directly abuts a sub-region of the hole injection and transfer layer 68, thus providing a path for electrons to recombine with holes outside of the emission layer 70.

FIG. 7B illustrates a second portion 104′ of an organic light emitting diode similar to that shown in FIG. 6B and configured to be joined to the first portion illustrated in FIG. 7A. FIG. 7C illustrates an organic light emitting diode 106″ formed by annealing a first part and a second part of a common layer of the first and second portions shown in FIGS. 7A and 7B. As shown in FIG. 7C, the assembled OLED 106″ includes both the spacers structure described in connection with FIGS. 6A through 6C, and the bank structure described in connection with FIG. 7A.

Aspects of the present disclosure provide for annealing two parts of a common layer that meet at an intralayer interface to join together first and second portions of an OLED. For example, the common layer can be an electron transfer layer. In implementations where the design parameters of the OLED provide that the electron transfer layer is the thickest layer of the OLED, utilizing the electron transfer layer as the common layer can be advantageous because the two parts of the common layer separately deposited on the first portion and the second portion are thicker than if another layer is utilized as the common layer.

Aspects of the present disclosure can also be applied to OLEDs in a multi-stacked structure. In a multi-stack OLED, a first portion of the multi-stack OLED is developed on a first substrate, and a second portion of the multi-stack OLED is developed on a second substrate. The two portions are then joined together to form the multi-stack OLED.

Aspects of the present disclosure also apply to color displays. Individual OLEDs can be formed (“manufactured”) according to the present disclosure with a color filter introduced between the emission layer 70 and the exposed side 64 of the encapsulation substrate 60. In implementations where the OLED is configured to emit, for example, white light, color filters can be inserted to provide for emission of base colors of a color display such as, for example, red, green, and blue filters. Additionally or alternatively, the OLED can be configured (such as by choice of the compositions and/or thicknesses of the plurality of layers in the OLED) to emit particular colors of light, and a pattern of different colors can be repeated across a display to form a color display having, for example, red, green, and blue color components.

Aspects of the present disclosure provide a method of manufacturing an OLED by separately forming opposing terminals of the OLED on two separate substrates, developing a plurality of layers of the OLED on one or both of the two terminals, and joining together the two portions. OLEDs manufactured by this process offer advantages over existing OLEDs, because both terminals are deposited on the respective substrates. Electrical connections to each terminal of the OLED, such as an electrical connection to a terminal of a driving transistor, do not rely on separate contacts that must be carefully aligned and which can require pressure to maintain efficient charge transfer. In particular, the cathode terminal can be directly deposited on the drain terminal of an n-type thin film transistor acting as a drive transistor. Such a configuration allows the drive transistor to drive current through the formed OLED while the gate-source voltage of the drive transistor (“Vgs”) is unaffected by the operating voltage of the OLED. In particular, a shift in the operation voltage of the OLED (“V_(OLED)”) over the lifetime of the OLED does not impact the voltage Vgs applied across the drive transistor. OLEDs formed according to aspects of the present disclosure provide a reverse OLED configuration such that the cathode of the OLED can be securely coupled (e.g., by a deposition, evaporation, or similar process) to a drain terminal of an n-type drive transistor. Aspects of the present disclosure can also be applied to forming an OLED with an anode terminal deposited on a source terminal of a p-type drive transistor.

While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims. 

What is claimed is:
 1. A method of manufacturing an organic light emitting diode having a first terminal, a second terminal, and a plurality of layers between the first terminal and the second terminal, the method comprising: forming, on a first substrate, the first terminal of the organic light emitting diode; forming, on a second substrate, the second terminal of the organic light emitting diode; developing a first portion of the plurality of layers on the first terminal; developing a second portion of the plurality of layers on the second terminal; joining the first portion of the plurality of layers to the second portion of the plurality of layers such that the plurality of layers is situated in between the first terminal and the second terminal, wherein the plurality of layers includes a common layer having a first part included in the first portion of the plurality of layers, the common layer having a second part included in the second portion of the plurality of layers, and wherein: the developing the first portion of the plurality of layers includes depositing the first part of the common layer, the developing the second portion of the plurality of layers includes depositing the second part of the common layer, the joining is carried out by annealing the first part and the second part of the common layer, the common layer is an electron transfer layer.
 2. A method of manufacturing an organic light emitting diode having a first terminal, a second terminal, and a plurality of layers between the first terminal and the second terminal, the method comprising: forming, on a first substrate, the first terminal of the organic light emitting diode; forming, on a second substrate, the second terminal of the organic light emitting diode; developing a first portion of the plurality of layers on the first terminal; developing a second portion of the plurality of layers on the second terminal; joining the first portion of the plurality of layers to the second portion of the plurality of layers such that the plurality of layers is situated in between the first terminal and the second terminal, prior to the joining, placing a first spacer on the first portion of the plurality of layers and a second spacer on the second portion of the plurality of layers, and wherein during the joining, the first spacer abuts the second spacer so as to prevent the plurality of layers from being compressed.
 3. A method of manufacturing an organic light emitting diode having a first terminal, a second terminal, and a plurality of layers between the first terminal and the second terminal, the method comprising: forming, on a first substrate, the first terminal of the organic light emitting diode; forming, on a second substrate, the second terminal of the organic light emitting diode; developing a first portion of the plurality of layers on the first terminal; and developing a second portion of the plurality of layers on the second terminal; joining the first portion of the plurality of layers to the second portion of the plurality of layers such that the plurality of layers is situated in between the first terminal and the second terminal, wherein the developing the first portion of the plurality of layers or the developing the second portion of the plurality of layers includes placing a bank at a periphery of a hole transfer layer so as to prevent the hole transfer layer from abutting an electron transfer layer. 